Optimizing the strength-ductility balance in Co-free dual-phase compositionally complex alloys via nacre-like microstructures and hierarchical precipitates

Developing Co-free compositionally complex alloys (CCAs) with exceptional strength-ductility balance is essential for advancing high-performance structural materials, addressing the economic and resource limitations of Co-bearing counterparts. This study explores novel Co-free dual-phase (FCC+BCC) Fe₃₀Cr₃₀Ni₃₀Al₇Ti₃ CCAs featuring bio-inspired nacre-like microstructures to achieve enhanced mechanical performance. Within these architectures, FCC- and BCC-dominated regions are aligned along the rolling direction, forming a dual-phase matrix with embedded multi-scale hierarchical precipitate ensembles. The FCC-dominated regions exhibit a small quantity of unevenly distributed L1₂ nanoprecipitates, while submicron ordered B2 and L2₁ co-precipitates at grain boundaries create complex triple interfaces, effectively impeding crack propagation. Specifically, the BCC-dominated regions exhibit a complex arrangement of nanoscale B2 nanoprecipitates, submicron L2₁ precipitates, and microscale L1₂-strengthened FCC phases, establishing a unique and sophisticated microstructural framework. This innovative design achieves an exceptional ultimate tensile strength of ∼1.63 GPa and an elongation of ∼15.3% even after high-temperature annealing at 1273 K, surpassing the conventional strength-ductility trade-off and outperforming other Co-free CCAs under comparable conditions. The superior mechanical properties are attributed to the synergistic effects of the grain-refined lamellar FCC+BCC dual-phase framework with multi-scale precipitates, which collectively provide structural stability, precipitation strengthening, and hetero-deformation-induced strengthening. This work introduces a high-performance Co-free CCA and offers a strategic approach for designing advanced CCAs through bio-inspired hierarchical microstructures.